Solid oxide fuel cells typically operate at high temperature conditions. Because of these temperature conditions, solid oxide fuel cells typically require a supply of purge gas during various stages of operation. During start-up and shutdown of a solid oxide fuel cell, it is preferable not to flow gaseous fuel through a fuel cell, as it is potentially explosive at these lower temperatures. However, without the maintenance of a reducing environment in the region of the anode, the anode may be susceptible to oxidation, thereby compromising electrochemical performance and/or service life of the fuel cell. As such, during start-up and shut down conditions, it is not only important to avoid exposure of solid oxide fuel cell components to an atmosphere which is oxidizing, but it is also important to prevent their exposure to a potentially explosive atmosphere.
To mitigate these conditions, purge gas systems have been developed to supply solid oxide fuel cells with purge gas during start-up and shutdown conditions. An example of such a system is described in U.S. Pat. No. 5,928,805 issued to Singh et al. In Singh et al., the purge gas is generated by combusting a hydrocarbon fuel in the presence of air to generate a non-explosive mixture of combustion products, to which stored hydrogen is selectively added to maintain the desired hydrogen concentration in the final gas stream entering the solid oxide fuel cell. To generate the desired cover gas composition in this case, the flow of reactants entering the burner must be carefully controlled in order to form a combustion product whose hydrogen content is able to be attenuated to a desired level by selective addition of hydrogen from a separate supply source.